Detailed via Reddit, you can see a partial list of the patch notes below. The main new feature is the addition of Spectre, a Specialist returning from Black Ops 3. Multiplayer maps Masquerade, Artifact, and WMD have been added. Blackout map, Wetworks, update is live, flooding several areas on it to change things up. In regards to Zombies, a new Gauntlet comes with the update, Super Blood Wolf Moon. Some of the updates are available first on PS4 (they are specified in the notes).

Call of Duty Black Ops 4 is available now for PlayStation 4, Xbox One, and PC. The update is live now on all platforms, with the PS4 exclusive content coming at a later date to the other platforms.